PyQt >= 5.8 stops parsing stylesheet when it sees ~=

Qt >= 5.8 stops parsing stylesheet when it sees ~=

Previously working code (5.7.1 and earlier) now broken. It sets a single large stylesheet on the top widget then dynamically sets a property on widgets which receive styling via ~= in the sheet, e.g.

QWidget[style_class~='unfocused_pane'] {
    border-color: blue;
    border-width: 3px;
    border-style: solid;
}

Here's a minimal PyQt exmaple (also attached to this report)
https://gist.github.com/tbnorth/76191db825cc49dcca296ffb8d777047